This IHTC Digital Library (IDL) contains the keynote and general papers presented at the 15th International Heat Transfer Conference (IHTC-15), which was held very successfully with nearly 1200 participants in Kyoto, Japan during 10-15 August 2014. The program of IHTC-15 was started with an invited lecture and a traditional Fourier lecture in the first plenary session, and then, in succeeding parallel sessions, 29 invited keynote lectures and 698 contributed papers were presented.

Heat transfer, a major academic discipline originating from seminal studies of thermal non-equilibrium phenomena, has grown to include the science of transport phenomena for ions, electrons, and chemical species. This discipline deals with essential fundamentals such as energy, materials, food and water, and also with a range of technologies that support modern lifestyles. Heat transfer is now a vitally important field, as scientists and engineers face difficult challenges: development of cutting-edge technologies for highly efficient energy systems, massive information/communication equipment, high-value-added manufacturing, and for comfortable living environments, to name just a few. Due to its enormous scope and impact, the field of heat transfer is often called "thermal science".

For more than 60 years, IHTC events, nicknamed "Heat Transfer Olympics," have achieved worthy goals by offering unique opportunities for scientists and engineers to gather together, exchange state-of-the-art knowledge, and develop personal networks. The Organizing Committee has kept IHTC traditions while improving certain aspects, so that IHTC-15 will meet the requirements of the rapidly changing scientific environment in the 21st century. First, the International Scientific Committee employed a rigorous review process for submitted manuscripts to ensure that the archive of contributed papers will be of journal quality. As a result, from the initially received collection of more than 1300 extended abstracts, about 700 full papers were finally accepted. To facilitate lively discussions, all of these papers were presented in oral sessions, unlike the poster sessions of previous IHTCs.

In addition to exploring traditional research areas, IHTC-15 posed an important question in order to better serve society: "What is the role of thermal science in meeting societal challenges?" Clearly, we face major issues such as ensuring sustainable development, maintaining healthy ageing, providing sufficient food for all, and stimulating economic growth, and we need to develop scientific and technological solutions. Therefore, we have invited a prominent scientific leader, Professor Hiroyuki Yoshikawa, to deliver the first invited lecture on "Science of Scientific Advice", which was followed by the two panels on "The Role of Thermal Science in Meeting Societal Challenges" and "The Role of Thermal Science for Nuclear Disaster Resilience". Fruitful panel discussions have been summarized as messages from the panels. This sort of broader discussions will hopefully be continued in the future IHTCs. (The presentation materials in these special sessions are available at the web site of IHTC-15.)

Finally, I would like to acknowledge the Science Council of Japan, the Heat Transfer Society of Japan, the International Centre for Heat and Mass Transfer, and numerous cooperating technical societies and companies, for their generous supports. I would also like to express my sincere thanks to the members of the Assembly of IHTCs, all IHTC-15 Committee members, the secretariat, and student aids, for their enormous contributions in organizing and running the outstanding IHTC-15.